Exodus 17:8 - Coke's Commentary on the Holy Bible

Then came Amalek— We learn from Deuteronomy 25:18 that the Amalekites fell upon the hindmost part of the Israelitish army, and smote all that were feeble behind, at a time when they were all faint and weary at Rephidim. After this attack upon the rear, they came to a pitched battle in the plain below Mount Horeb, Exodus 17:10. The Amalekites inhabited some part of Arabia Petraea, near Rephidim, between that place and Canaan. They were descendants of Esau; and are therefore supposed to have hated the Israelites, the descendants of Jacob; whose settlement in the land of Canaan they, perhaps, were desirous to prevent, as imagining they themselves had an equal right to it.